The treatment of metallic water-circulating apparatus such as those employed in steam generating plants, heating systems, cooling water circuits and waterpipe systems to protect them against the corrosive action of water has been an industrial practice for a long time. The treatment is directed primarily towards the protection of the base metals used for the fabrication of such apparatus, chiefly steel, brass, aluminum, zinc and galvanized steel. Among the agents used for the purpose are the long-chained aliphatic amines described in U.S. Pat. No. 2,460,259. But with these amines it is only possible to obtain a sufficient corrosion-preventing effect when they are present in relatively high concentrations, which raises a number of problems in their application. The aliphatic amines, particularly the long-chain fatty amines, are solids at room temperature and must be brought into a liquid, easily dilutable form. The very poor water-solubility of the corrosion-inhibiting aliphatic amines requires in practice the production of dispersions with additional dispersing aids (U.S. Pat. No. 3,088,796), but both the dispersing aids and also the fatty amines themselves can cause considerable foaming in circulating systems.